Gain-controlling circuits



Feb 23 1926.

S. B. WRIGHT ET AL GAIN CONTROLLING CIRCUITS Filed April 30, 1925 v www.A Ni W E f acum u .VII H. D P.

M. l w ls m m O M T m 7 m V BYV Patented Feb. 23, 1926.

UNITED` STATES 1,573,891 PATENT OFFICE.

SUMNER B. WRIGHT, OF EAST ORANGE,

NEW JERSEY, AND JOHN 'I'. SCHOTT, OF

BROOKLYN, NEW YORK, ASSIGNORS T AMERICAN TELEPHONE AN D TELEGRAPB.'COMPANY, A. CORPORATION OF NEW YORK.

GAIN -CONTROLLING CIRCUITS.

Application led April 30, 1925.

To all whom 'it may concern Be it known that ive, SUMxnn B. IVRIGHT andJoris T. Scno'rr, citizens of the United States, residing at East Orangeand Brooklyn, in the counties oi Ilssex and Kings and States of NewJersey and New York, respectively, have invented certain Improvements in(tain-Controlling Circuits, ot' which the following is a specification.

This invention relates to telephone transmission circuits and moreparticularly to arrangements l'or controlling the gain of telephonerepeaters.

In certain cases it is desirable to transmit a relativelyY high andsubstantially constant volume over a transmission circuit from allsubscribers. For exan'iplc, in the case of a radio telephone transmitterit is necessary to radiate a practically constant volume in 0 order tolieep the voice currents strong as compared to noise. Since certainsubscribers may be connected to such a radio telephone transmitter overlong circuits having large losses, while other subscribers may 25 beconnected over relatively short circuits, and since regardless ot' thelength of the circuit .some subscribers talk much louder ythan others,it is necessary to adjust the gain otan amplifier associated with theradio transmitter for the different conditions met with it' the volumeradiated is to be maintained constant. In circuits arranged to meet sucha requirement'. some method must he provided to insure that when thecircuit is adjusted for a large repeater gain to amplify the weakcurrents, strong currents such as those put out by operators near theinput ot the circuit will not exceed the value for Which the circuit isadjusted, otherwise serious distortion or other harmful effects mayoccur.

It is one of the objects ot this invention to provide a circuitarrangement whereby when an operator comes in on a circuit of the typeabove described near the point at which the variable gain repeater isprovided, the gain Will be reduced to a value such that the volume ofenergy re ulting from the operators speaking on the circuit Will notexceed the limiting value for the circuit.

Other and further objects of the invention will be clear from thefollowing detailed description when read in connection Seria No. 27,001.

with the accompanying drawing, the ligure ot which illustrates a circuitdiagram embodying the principles of the invention.

Referring to thedrawing, SL represents a subscribers line which may beconnected to a four-wire repeater llink comprising paths LE and LIVthrough the usual hybrid coil l() and balancing network N. The path LIfVincludes a transmittingr amplifier AIV and the path LE includes areceiving amplitier AE. The path LIV may be connected to a suitableradio telephone transmitter and the path LE to a corresponding radiotelephone receiving circuit. The subseribers line SL is connected to thehybrid coil through a trunk TL and in order that different lines may beconnected with the trunk, the line SL and the trunk TI, terminate injacks J1 and J2 respectively, adapted to cooperate with the plugs P1 andP2 of a toll operators cord circuit.

In order to adjust the gain of the amplifier AIV so that the volume ofenergy transmitted over the circuit LIV may be maintained at asubstantially constant value, a potentiometer ll is associated with theinput side of the amplifier. This potentiometer ll may be adjusted bysteps determined by the gain control dial GC whose cent acts B to Kinclusive are connected to close circuits through individual relays B toK, inclusive. These relays in turn establish connections from variouspoints on the potentiometer il to the amplifier AIV. For simplicity, therelays C to H inclusive and their connections are not illustrated. Thegain control dial may be manipulated by a technical operator at atechnical operators position. A volume indicator VI is provided on theoutput circuit of the amplifier AIV to indicate to the technicaloperator the amount of volume being transmitted from the amplifier.

The technical operator is provided with a cord circuit terminating intwin plugs 1) and PJx adapted to co-operate with twin jacks J., and J4connected in the trunk TL. The technical operators cord circuit isprovided with a telephone operator's set which may be'connected to thecord by means of key K3. 'lhe back plug I),l of the cord may be insertedin the jack J, when the technical operator desires to speak over theline LIV at such times as no line such as SL is connected to the trunkthrough the toll operators cord circuit. lf, however, such a connectionis established with the toll operators cord circuit, the technicaloperators cord circuit may have its front and back plugs P3 and P4inserted in the jacks J 3 and J 4 respectively so that the connectionwill extend through the technical operators cord circuit. A specialrelay A is provided in the gain control circuit and the circuit of thisrelay is under the joint control of the key K3. of the technicaloperators cord circuit and the key K, of the toll operators cordcircuit. It either operator goes in on the circuit With a telephone setby operating the key K, or keyK3 as the case may be, the

relay A, which is normally energized When either cord circuit is in use,will be released during the time that the operators tele-- phone set isconnected to the cord circuit and will close a circuit for a specialadjustment of the potentiometer 1l, which will bring the gain of theamplifier AW down to a point such that When the operator talks, thevolume of energy transmitted over the circuit LV will not exceed themaximum limit. At the same time, the relays B to K inclusive are allplaced in an inoperative condition so that the setting of the potenti-.ometer 1,1 will not under these conditions be determined by the settingof the gain control dial GC. Y

Further details of the invention will now be clear froma description ofthe operation 'F which is as follows: The toll operator will establish aconnection from a line such as SL to the radio transmitter associatedWith the circuit LW by inserting'the 'front and back plugs P, and B2 ofher toll cord circuit in the jacks J1 and J 2 respectively. A circuit isnow established from battery, over the back contact of the relay M,sleeve conductor of the back plug P2, sleeve conductor of the jack J 2,over contacts 15 and 1G of jacks J 3 and J 4 to conductor 17. Relay A,Which has one. terminal of its winding connected to the conductor 17 andthe other terminal connected to ground, will be energized and Will openthe circuit 18. At the same time, one of the relays B to K inclusive, asdetermined by the setting of the gain control GC, is energized andconnects a point of the potentiometer ll tothe input transformer of theampliiier AW. As soon as the subscriber begins to talk over the circuit,the volume transmitted from the ampliiier AW will be indicated by thevolume indicator Vl so that the technical operator may adjust the gaincontrol dial GC to bring the volume to the desired level. For example,it the subscriber talks in a weak voice over a long telephone line thevolume indicated by the volume indicator Vl will be quite low and thegain control dial will be set upon its high contact B,

thereby closing a circuit from ground through the Winding of the relay Bto the conductor 17. The relay B is energized and connects the upperterminal of the input Winding of the transformer over the front contactof the relay B to the upper terminal of the potentiometer 1.1. lf,however, the volume of current incoming lrom'the line SL should begreater, the gain control dial might be set to a lower contact, such asJ, in which case the relay J would be energized and close the circuitfrom the input transformer to a lower setting ot the potentiometer. ltwill be noted that the circuits of all of the relays A to K inclusiveextend over the sleeve conductor ot' the jack J 2 to a battery in thesleeve circuit of the back cord of the toll operators cord circuit.

Suppose now, with the gain control set upon contact B so that the relayB is operated for the corresponding setting of the potentiometer l1, thetoll operator should desire to speak over the circuit. The key K1 Willthen be actuated to connect the toll oplerators telephone set to thetoll cord. e operation of the key vlli, closes a circuit of the relay Massociated with the toll cord, which relay in turn opens the sleeveconnection to the QA-volt battery. T his removes battery from thesleevev conductor ot' the trunk and consequently from the conductor 17.The relay B or any other relay of the set of relays B to l inclusivewill be deenergized so that these relays no longer control the settingof the potentiometer. rlhe relay A will also be deenergized at the sametime and will close a circuit over its back Contact from the upperterminal of the input transformer, through the conductor 18, to a pointon the potentiometer ll such that the volume ot energy due to theoperators speech as indicated on the volume indicator VI will notelvceed the limits for the. circuit. lf at a time when the connectionthrough the operators toll cord is not establisln-d` the technicaloperator should desire to speak over the circuit, the technical operatorwill insert the back plug B, into the jack J4, thereby opening theconnection to the sleeve conductor of the jack J2 at the contact 1G andconnecting the tip and ring conductors leading from the hybrid coil tothe tip and ring conductors of the technical operator-s cord circuit.The conductor 17 is also connected over the sleeve conductor ot the twinjack and the sleeve conductor of the twin plug and thence over a contactof the key K3 and a contact ot the relay l, to a Q-l-volt battery. Acircuit is thus established troni the Q4-volt battery for one ot therelays l to l( inclusive, depending upon the setting oi the gain controldial at that time. lihen the operator throws the talking key liz., 1oconnect the telephone set to the technical operators cord circuit, thebattery convce nection tothe sleeve conductors of the twin plug P4 isopened at contact 19, thereby releasing the relay of the group ll to Kinclusive which is atthe moment actuated t-o open the potentiometerconnection then established. At the same time thel relay A isdeenergized and establishes the. normal potentiometer connection throughthe conductor 18, bringing the volume level back to the level desirablefor the conreisation oi an operator.

It, when a connection is established through the toll operators cordcircuit', the technical operator desires to come in on the circuit,plugs 1) and I), of the technical operators cord circuit will beinserted in the jacks J3 and J,l respectively. The normal tip and ringconnections through the twin jacks J?, and J,t are now broken and thetip and ring connections are established through the technicaloperato1"s cord circuit. The connection from the sleeve of the jack J2to the conductor 17 is also broken and conductor 17 is connected overthe S contacts of the twin jack J ,E and the corresponding S contacts ofthe twin plug P, and over the contact 19 ofthe key K3 to the armature ofthe relay L. A circuit is also com-- pleted from the AZ4-volt batterythrough the winding of the relay L, contact RS of the twin plug P3 andcorresponding contact of the jack J3 to ground. The relay L beingenergized, the circuit previously traced from the conductor 17 to thearmature of the relay L is extended over the TS contacts ot the twinplug P3 and twin ackJ, over the sleeve contact of the jack J2 andplugP2,and thence over the back Contact of the relay M to the 2t-voltbattery connection at the toll operators position.

It will thus be seen that the controlling circuit for the relays A to Kinclusive extends through both cord circuits. Therefore, it' the tolloperator throws her key K, the relay M will be operated to release allot the. relays A to K inclusive, thereby breaking the setting of thepotentiometer as determined by the gain control dial and establishing asetting of the potentiometer over the conductor 18. Similarly, if thetechnical operator throws the key K,s the relay controlling circuit willbe opened at contact 19 with the same result. The operation of the keyK3 or key K, as the case may be docs not open the through connection asestablished by the cord circuits.

It will, of course, be obvious that any number of sets of twin jackssimilar to J 3 and J4 may be provided in the circuit at differentpositions and by using cord circuits at these points similar to thetechnical operators cord circuit any desired number of operators mayindependently come in on the circuit in the manner above described. Thisis for the reason that each cord circuit of the type shown at thetechnical operator`s position completes a sleeve connection over thetalking keys of successive cords in series so that the operation ot anykey will set the gain control circuit to normal without interruptingtransmission.

It will be obvious that the general principles herein disclosed may beembodied in many other organizations widely differentf'rom thoseillustrated without deiiartinpll from the spirit of the invention asdefined in the appended claims.

lVhat is claimed is:

l. In a signaling system, an amplifier, means to control thc gain ofsaid amplifier, a. cord circuit for establishing connections to saidamplifier, an operatorlsl telephone set associated with said cordcircuit, and means whereby when said operator-s telephone set isconnected in circuit the existing gain adjustment of said amplifier willbe disabled and the amplifier will be adjusted to the requirements ofsaid operators telephone set. y

2. .In a signaling system, an amplifier, a potentiometer having variablesettings for controlling the gain of said amplifier, a cord circuit'.for establishing connections to said amplifier, an operators telephoneset associated with said cord circuit, and means whereby when saidoperators telephone set is connected in circuit the existingpotentiometer connection is disestablished and a normal potentiometersetting dependent upon the requirements of said operators telephone setwill be established.

3. In a signaling system, an amplifier, meansfor variably adjustingr thegain of said amplifier, a plurality of cord circuits connected in tandemto establish connections to said amplifier, operators telephone sets foreach cord circuit, and means whereby when the operators telephone set ofany cord circuit. is connected in the circuit the existing gainadjustnnmt of said amplifier will be automatically disestablished and again adjustment conformingto the requirements of the operators telephoneset will be automatically established.y

4. In a signaling system, an amplifier, an adjustable potentiometer forvarying the gain of said amplifier, a plurality ot cord circuits adaptedto be connected in tandem to establish connections to said amplifier,operators telephone sets for each cord circuit, and means whereby whenan operators telephone set is connected in circuit, the existing settingof the potentiometer will be automatically disestablished and a settingcorresponding to the requirements of the operators telephone set will beautomatically established.

5. In a signaling system, an amplifier, a potentiometer, an adjustableswitch for variably setting said potentiometer to adjust the gai-n ofsaid amplifier, a cord eircuit for .establishing connections to saidamplifier, an opcrators telephone set associated with such cord circuit,means Whereby when the operators telephone set is connected in circuitthe settingof the potentiometer determined by said switch Will beautomatically disostablisl'ied and the potentiometer will beautomatically set to produce a gain in accordance with the requirementsof said operators telephone set.

6. In a signaling system, an amplifier, an adjustable potentiometer forcontrolling the gain of said amplifier, a gain control switch f adaptedto be variably set, a plurality of relays selectively energized inaccordance with the setting` of said switch, each relay controlling anindividual setting ot said pot-entiometer, an additional relaycontrolling the normal setting of said potentiometer, a cord circuit forestablishing connections to said amplifier, an operators telephone setassociated with said cord circuit, and a circuit for said relaysextending to said cord circuit and controlled thereby whereby when theoperators telephone set is 'connected in circuit the circuit of saidrelays Will be changed to disestablish the potentiometer settingdetermined by the selective relays and to establish the normal settingcontrolled by said additional relay.

In testimony whereof, We have signed our naines to this specificationthis 29th day ot April, 1925.

SUMNER B. VRIGHT. JOHN T. SCHOTT.

